#include <stdio.h>	// for FILE *

enum Token_type {
    TOKEN_INVALID,	// an error
			// put invalid token into Token.str
			// Examples: &

    TOKEN_LINE_LABEL,	// a label on a line, in the first column
			// labels start with [a-z_], followed by [a-z0-9_]
			// will be no more than 80 characters long
			// put label into Token.str
			// Examples: buf_23, BIG_BUF

    TOKEN_OPCODE,	// an opcode (or a pseudo-op)
			// Not in first column (that would be TOKEN_LINE_LABEL)
			// put which one into Token.opcode
			// Examples: ADD, brz, Ret

    TOKEN_COMMA,	// a comma
			// Example: ,

    TOKEN_INT,		// An integer, whether hex or decimal
			// put the value into Token.val
			// Example: -12 (decimal), #34 (decimal), xB01c, xDEAD

    TOKEN_REGISTER,	// put the number (0-7) into Token.val
			// Examples: R0, r1, ... R7

    TOKEN_LABEL,	// a label as an operand (e.g., BR foo)
			// Not in the first column.
			// Otherwise, same rules as TOKEN_LINE_LABEL
			// put label into Token.str
};

enum Token_opcode {
    OPCODE_ADD,
    OPCODE_AND,
    OPCODE_BR,
    OPCODE_BRZ,
    OPCODE_JMP,
    OPCODE_JSR,
    OPCODE_JSRR,
    OPCODE_LD,
    OPCODE_LDI,
    OPCODE_LDR,
    OPCODE_LEA,
    OPCODE_NOT,
    OPCODE_RET,
    OPCODE_ST,
    OPCODE_STI,
    OPCODE_STR,
};

struct Token {
    int line_number;		// first line is 1
    enum Token_type type;
    enum Token_opcode opcode;	// TOKEN_OPCODE
    char *str;			// TOKEN_INVALID, TOKEN_LINE_LABEL, TOKEN_LABEL
				// Must be dynamically allocated
    int val;			// TOKEN_INT, TOKEN_REGISTER
};

// Scan the next token.
// Return NULL at end of file.
// Otherwise, allocate a struct Token, fill it in, and return it.
struct Token *scan_token(FILE *);

// Free all the memory allocated by scan_token().
void free_token(struct Token *);